Establishing crank end float

[Jono]

I have my engine components back from machining and will shortly be embarking on a dry build to check pistons to deck height and other matters.

This is a 1300GT which showed moderate wear on the existing crank thrusts. I want to order new thrust from Minspares and have a couple of questions for the wise old owls of this forum:

1 Is there a particular grade of thrust I should purchase for a fast road engine (using orange diaphragm)
2 Can I measure using the existing worn thrusts and establish a new thrust washer oversize/thickness or do I have to obtain a range of sizes and go with best fit?
3 What are the views on optimum end float/range of float I should be aiming for?

On another matter, what is the best way to ensure a scrupulousy clean block? It's been hot tanked but the oil plugs have not been pulled. I intend to pull the oil plugs and clean out the galleries - would a chemical dip be best to ensure this? Also, is it okay to have it chemically dipped after the bores have been honed (as they have).

Many thanks

Jon

[Spider]

If the old thrusts aren't sored, or badly worn, there's no reason why you can re-used them, after all the faces are now matched to your crank and they are oil soaked, though if there is excessive end float then you'll want to replace them for sure. I will add to that, that I do fit new thrusts nearly every time.

With new ones, they are nearly all stamped on the back with various numbers etc. These don't let the thrusts sit flat, as a matter of habbit, I take to the backs of them with a diamond lap, make sure they are dead flat then.

I aim for 0.003 to 0.005 end float on a road car with a red line around the 6000 - 6500 mark, however if it's likely to sit at higher revs for extended periods, then add at least another thou to those numbers.

As for the grade of thrust, I prefer a softer (stock) type as the thrusts are cheaper than a new crank or even getting the thrust faces re-ground.

In regards to cleaning the block, as long as the Cam Bearings haven't been fitted, you should be OK with a Chemical dip of most types, it won't affect the bore finish.

[Jono]

Spider,

Perfect - many thanks.

Regards

Jon

[Jono]

I've measure the crank end float at it's only 1.5 thou with the old thrust washers in place.

This seems rather tight, is it okay?

Jon

[Spider]

That is tight - too tight.

Take the thrusts out and give the back (steel side) a few rubs on a diamond lap or fine oil stone, to take any high bits off, however, if they are the old ones, you may need to have the backs ground.

Are you checking with a feeler gauge? Try it with a Dial Gauge and use a lever - gently - on the crank to move it back and forth. You'll get a considerably more accurate result.

[Jono]

Thanks Spider - that was using a dial gauge and levering the crank.

I will rub them down but I am surprised that the float is so tight on the original set up.

I am not sure what to expect but the existing thrust faces are worn down to copper - is that normal or a symptom of too little end float?

Jon

[Spider]

Ah, OK, well your measurement is as accurate as can be.

Most Thrusts are actually bronze but have a high copper content, when looking at them, they do usually have a copper appearance, so that sounds fairly normal.